This invention relates to a power-driven stapler for performing stapling operations and more particularly to a power-driven stapler in which unformed staple elements are automatically fed successively by a power motor to a staple forming and driving unit so that each staple element is formed into a U-shaped staple and then is driven through an article to be stapled.
The type of power-driven or electrically-actuated stapler in which each unformed staple element is formed into a U-shaped staple and then is driven through an article such as sheets of paper is disclosed in U.S. Pat. No. 4,623,082, owned by the assignee of the present invention. Such conventional electric stapler employs an electric motor as drive means and actuating links which are driven by the motor. A staple forming and driving unit connected to one end of the actuating links through respective springs as well as a magazine are vertically moved so as to drive each staple through the article to be stapled. A predetermined number of unformed staple elements are adhesively bonded together in the form of a sheet, and a plurality of such sheets are stacked one upon another within a staple cartridge. The stack of staple element sheets are sequentially fed toward the staple forming and driving unit by an endless belt serving as a staple feeder, with the lowermost sheet being fed out first, so that each staple element is formed into a U-shape and then driven through the article to be stapled. Then, the legs of the U-shaped staple extending through the work are folded by a clinching means.
The actuating links are pivotally mounted on a base of the stapler intermediate opposite ends thereof, and have a first end engaged with the magazine. A motor-driven cam plate acts on the second end of the actuating links so that the magazine is moved vertically, that is, upwardly and downwardly. When it is desired to increase the stroke of the vertical movement of the magazine to increase an insertion opening for insertion of the article to facilitate the insertion of the article in its stapling position, in this conventional construction, the stroke of the vertical movement of the second end of the actuating links needs to be correspondingly increased. As a result, the overall size of the stapler becomes large. To provide an overall compact construction of the stapler, it is necessary to either shorten the actuating links or decrease the size of the cam plate. However, if the actuating links are reduced in length, the cam plate needs to be larger, so that the eccentricity of the cam plate is correspondingly increased. On the other hand, if the cam plate is reduced in size, then the actuating links need be increased in length. Therefore, with these procedures, it has been difficult to provide a compact stapler.
Another difficulty with the above conventional stapler is that the staple forming and driving unit is forcibly returned to its upper dead point (i.e,. initial position) in accordance with the movement of the actuating links, so that even if a staple is jammed in a staple driver guide with, subsequent staples are sequentially fed to this driver guide path so long as the motor continues to rotate to actuate the actuating links. Thus, in the above conventional electric stapler, once a staple becomes jammed in the driver guide path, subsequent staples also become jammed successively, and the staples thus jammed and deformed give rise to damage to the driver guide path thereby preventing the proper movement of the stapler, and holding the staple driver against movement in the driver guide path which stops the rotation of the motor in its energized condition.
In conventional staplers of the type in which sheet-like staple elements are fed by an endless belt to the staple forming and driving unit from the staple cartridge, where a space or distance between an upper surface of the endless belt and a lower surface of a staple guide portion of the staple cartridge is almost equal to the thickness of the sheet-like staple element. The force under which the sheet of staple elements is urged against the upper surface of the endless belt is weak, and therefore the staple feed force is also weak. This may result in failure to properly feed the sheet of staple elements. If the above space between the upper surface of the endless belt and the lower surface of the guide portion is less than a half of the thickness of the sheet of staple elements, the sheet can not be discharged from the staple cartridge, thus failing to properly feed the sheet of staple elements. To overcome this difficulty, it has been necessary to keep the space between the upper surface of the endless belt and the lower surface of the guide portion in a range wherein at the low end the space is less than the thickness of the sheet of staple elements and at the high end more than half of this thickness. This requires high processing or machining precision.
U.S. Pat. No. 4,593,847 discloses a typical example of clincher devices of the type in which a pair of legs of a stapler extending through an article to be stapled are folded or bent against the back side of the article in parallel relation to each other. In such a clincher device, movable clincher members for pressing the staple legs against the back side of the article have recesses or grooves for receiving the staple legs. Therefore, the staple legs fail to be firmly pressed against the article at a final portion of the clinching operation, so that the folded or clinched staple legs are spaced from the back side of the article, which results in a relatively loose stapling.